The US Senate Finance Committee set a deadline Tuesday for UnitedHealthcare, Humana and CVS Health's Aetna to disclose detailed records on prior-authorization denials in their Medicare Advantage plans. The lawmakers demanded internal data on denial rates and appeals outcomes in a bipartisan inquiry.

The request followed letters sent earlier this week pressing the largest Medicare Advantage insurers over allegations that patients face improper delays and denials of medically necessary care. Roughly half of all Medicare beneficiaries are now enrolled in privately run Advantage plans, giving the companies outsized influence over care for older Americans.

Senators cited prior findings from the Department of Health and Human Services Office of Inspector General, which reported that some Advantage plans denied claims that would have been covered under traditional Medicare. Committee members asked the insurers to explain their use of algorithms and automated tools in coverage decisions and to detail how often denials were overturned on appeal.

A spokesperson for AHIP, the insurance industry trade group, said Advantage plans deliver better value and coordinated care to seniors and that prior authorization protects patients from unnecessary treatment. UnitedHealth Group and Humana said they would review the requests and cooperate with the committee.

The inquiry adds to mounting pressure on an industry already facing regulatory reviews of billing practices and risk-adjustment payments. The Centers for Medicare and Medicaid Services has separately proposed tighter rules on prior authorization, with a final decision expected later this year.